Such a driving device in the form of a lifting device is known from, for example, DE 35 22 823 A1.
In the following, the invention will be described on the basis of a tractor, the lifting device being formed by the so-called toolbar (hitch). Attachments are fixed to the toolbar, for example, a plough, a harrow or a mowing tool. By means of the drive, the attachments can then be brought to the right working height, so that, for example, a plough can be lowered by a predetermined depth into the earth.
However, the invention can also be used with other working vehicles and drives, for example, with scavengers, whose sweeping tool must be lifted or lowered.
In most cases, a single-acting drive is sufficient, as it is merely required to lift the attachment, which is fixed on the lifting device. When this attachment has to be lowered, this is done by means of the own weight of the attachment.
A double-acting drive is described in EP 0 838 140 A1. The drive shown in this document cannot merely lift the attachment, but is also used to perform a deliberate lowering.
In practice, double-acting drives are barely found on such lifting devices. Even though the manufacturing effort required for realising a double-acting drive is relatively small compared with a single-acting drive, single-acting drives are chosen, as the control of a single-acting drive is much easier for the user.
Based on the foregoing, it is the general object of the present invention to provide a simple way of extending the functionality of the lifting device.